The present invention generally relates to a method for starting turbine engines and more specifically to a tip impingement air starter for a turbine engine.
This invention relates to power plants and particularly to a gas turbine power plant that may be used for effecting propulsion of aircraft at high speeds. Such a power plant may include an air compressor, a combustion apparatus, and a gas turbine compactly arranged in series to keep the weight, overall length and diameter of the unit to a minimum. These parts may be built into the wing of an aircraft or mounted centrally within and supported by an outer casing of streamline form that directs the flow of air through the power plant.
The turbine is driven by the hot gases provided by the compressor and combustion apparatus and extracts at least sufficient power from these gases to drive the compressor. The remainder of the available power may be utilized to propel the aircraft by ejecting the gases from a propulsion jet rearwardly of the turbine.
Since the power plant relies on the power supplied to the turbine to operate the air compressor, it is not self-starting and some means must be provided for initially rotating the turbo compressor shaft. Starting gas turbine engines in an efficient manner has been a challenge virtually from the beginning of the use of turbine engines. The starters are used relatively infrequently, are required to convert large amounts of power, and must be carried along with the powerplant as dead weight.
Lightweight impingement air starters have been used in the past, but unfortunately were not efficient in their use of the supplied compressed air. Present day air starters are efficient but at the expense of weight, gearing complexity and cost. Present day air starters are also subject to mechanical breakdown.
It is thus highly desirable to provide an improved system and method for starting turbine engines. If is also desirable to simplify the design of impingement air starters for turbine engines and reduce weight, complexity and cost.
The present invention involves introducing a channel into the turbine case by which compressed air can be introduced from a pressurized air source to turn the High Pressure (HP) turbine, thereby turning the HP compressor, and enabling the gas turbine engine to be started. High pressure air is introduced through a channel in the turbine casing and expanded/accelerated by a series of diffusers. This high velocity air impinges upon at least one turbine bucket member that is located on the tip of a HP turbine blade. These turbine bucket members are preferably impulse-type turbine bucket members. After kinetic energy from the high velocity air is extracted by the turbine bucket members, the gas can be directed through a series of openings located upstream of the turbine blade and is directed to the airfoil section of the turbine blade to extract any remaining kinetic energy.
In an alternative embodiment, the channel in the casing is located close to an axial compressor in a gas turbine engine""s forward section. In this embodiment, one stage of an axial compressor in a gas turbine engine""s forward section is modified to incorporate a small turbine bucket member at the top of each compressor blade. Air is then introduced to the small turbine bucket member in a manner similar to that described above to start the engine. In addition, the configuration of this stage can be used to help recover gas energy.